The present invention is directed to methods of modifying surface properties of polymers with polymeric additives. Particularly, the invention is directed to methods of preparation and to polymers suitable for blood-contacting surfaces. The blood or tissue-contacting surfaces may be in the form of smooth surfaces or may be woven or knit. The present invention may also be applicable for preparing textiles having other specified surface properties, such as, oil resistance, water repellency and the like while also possessing launderability by virtue of the hydrophobic and hydrophilic groups of the polymeric additives and the additives surface activity.
Polysiloxanes are known to have a particularly low critical surface tension value and have been suggested for incorporation into polyurethanes to improve the surface characteristics of such materials. However, polysiloxane by itself is known to have a tendency to exude from the polyurethane base polymer as illustrated in Reischl et al U.S. Pat. No. 3,243,475.
Cross-linked, thermosetting polysiloxane-polyurethane block copolymers have been suggested for use as blood contact surfaces of biomedical devices as illustrated in Nyilas U.S. Pat. No. 3,562,352. The technique disclosed for such use includes fabricating the entire blood contact devices from such block copolymers or coating such devices with the copolymers. The block copolymers themselves may have poor structural characteristics due to a high proportion of polysiloxane. Furthermore, the coated materials are particularly expensive to form since they must be coated in a separate operation after the device is fabricated and are not processable by thermoplastic methods such as injection molding and extrusion. The manufacture of tubing, catheters and other blood-contacting disposable devices from such materials is particularly expensive due to the necessity of employing solution fabrication techniques.
Certain experimental work has been published relating to the blending of block copolymers of polydimethylsiloxane with other homopolymers. These materials are known to produce films with high siloxane surface concentrations. See, for example, D. G. Legrand and R. L. Gaines, Jr., Polym. Prepr. 11 442 (1970); D. W. Dwight et al, Polym. Prepr. 20, (1), 702 (1979); and J. J. O'Malley, Polym. Prepr. 18 (1977). However, these references do not describe the polymer blends as having characteristics which would be particularly advantageous in biomedical applications. In particular, silicone-containing polycarbonates have low contact angle hysteresis, a property, as discussed hereinbelow, which may render them unsuitable as a blood contact surface.
Minor amounts of block copolymers including segments of polydimethylsiloxane and homopolymers of polycarbonate, polystyrene, poly-(2,6-diphenyl-1,4-phenylene oxide), and polyamide-imide have been blended with base homopolymers for modifying the surface properties of the homopolymers. Gaines et al U.S. Pat. No. 3,961,122 suggests using such surface modified polymers as thin films, while Gaines et al U.S. Pat. No. 3,686,355 suggests a variety of uses including bulk uses. These patents, however, do not disclose polymer blends possessing the desired overall physical properties for biomedical applications of excellent flexibility and softness, while also possessing excellent strength.